I think you're misunderstanding what is meant by updating moves to the 8th generation. Moves that existed in Generation V (aka moves that can be pulled from ROMs) are in the game and updated to modern learnsets. Any move introduced in Generation VI beyond is not in the game at all. (Ex: Moonblast, Liquidation, Body Press) BUT, something like Shell Smash (Generation V move) that was given to Blastoise in Generation VIII exists in its mvoeset.
The only exception I can think of to something like this is the devs recently adding a Slush Rush equivalent to the Beartic line, though it has a different name.